Infections of orthopedic implants
are associated with high morbidity. The emergence of antibiotic resistant
strains and the tendency of microbes to form biofilms on orthopedic devices
prompt the individuation of novel antimicrobial agents. Silver nanoparticles
represent an interesting alternative, but their effects on bone cells need to
be clarified. We focused on osteoblast-like cells and on bone
marrow-mesenchymal stem cells and found that these cells are rather resistant
to the cytotoxic effects of silver nanoparticles, with a half maximal
inhibitory concentration around 25 µg/mL as detected by MTT assay. Within a
month of treatment, osteoblast-like cells adapt to the presence of the
nanoparticles by upregulating hsp70 as shown by western blot. Hsp70
overexpression correlates with the restoration of normal cell proliferation. No
alterations in the extent and time requirements were detected in mesenchymal
stem cell induced to differentiate in osteoblasts in the presence of silver
nanoparticles. Because the concentrations of silver nanoparticles which show
antimicrobial activity are lower than those exerting toxic effects on
bone-forming cells in vitro, we suggest that silver nanoparticles might represent
a challenging tool to fight infections in orthopedic implants.